Studies on the Effect of Burden on Blast Damage and the Implementation of New Blasting Practices to Improve Productivity at KCGMs Fimiston Mine

Wall control blasting practices arc necessary to reduce the impact of blasting on mine faces but can also have a significant negative impact on mine productivity and operating costs. The conventional practice in deep open pit mines is to use so-called trim blasts adjacent to pit walls. To provide burden relief these trim blasts have fewer rows than full production blasts and are fired to a cleared free-face: hence they are termed 'unchoked.' This practice leads to scheduling constraints on the pit operations and can cause ore dilution due to excessive muckpile movement. The use of such trim blasts stems from the perception that increased wall damage results from 'choked' blasts. These concerns are based on the unproven assumptions that blast vibration levels and explosive gas penetration increase with increased blast burden and face confinement. This paper describes work undertaken as part of a major investigation into wall control blasting at the KCGM Fimiston Mine, Kalgoorlie, Western Australia. It details a study to assess damage effects due to blast burden. Borehole air pressure measurements and borehole video camera inspections owere done behind a series of single blastholes drilled owith varying burden distances, as owell as behind a dedicated trim blast and a full production blast. It was found that the measured damage effects, including visible rock cracking, dilation, and the limited extent of gas penetration behind the blastholes, did not vary significantly with burden or blast type for the cases tested. This result was in complete agreement with detailed vibration measurements conducted by Blair and Armstrong [1] during the study, which found that vibration was independent of blast burden. As a result of these investigations, changes to the blasting practices at the mine were implemented. Dedicated trim blasts and free-face blasting have been replaced by modified production blasts and the practice of 'choking' blasts has been introduced. This has resulted in a significant improvement in productivity and cost savings without compromising pit wall integrity.     

Wall Control Blasting Practices at BHP Billiton Iron Ore Mt Whaleback

A programme of blast improvement was initiated at the Mt Whaleback iron ore mine by BHPIO management in early-1998. One component of that work was the need to improve wall control blasting practices to better achieve the designed pit slope elements. This paper describes the geological conditions in which pit walls are developed, the mine operating equipment, the blast design concepts applied to minimise blast damage, the techniques applied in an assessment of the blast performance and the operational procedures developed to ensure that the blast concepts are effectively implemented in the production environment. Substantial changes have been implemented in both technical and operational aspects of the mining operation in order to achieve the improvements in pit wall condition, in particular recognising the need for a more flexible approach to limits blasting in response to highly variable and complex geology. The benefits to the mine are not only an improved wall condition, but increased confidence on the part of mine management that mine plans may be implemented on design and on schedule.     

The role of non-linear deformation analyses in the design of a reinforced soil berm at Red River U-frame lock No. 1

This paper describes a design application of non-linear deformation analysis to a complex soil–structure–foundation interaction problem through use of a finite element analysis. The problem consists of a proposed renovation to an existing soil-founded U-frame lock structure consisting of construction of a densely reinforced soil berm adjacent to an existing lock wall. Major questions facing the designer involve reduction of the earth pressure on the lock wall, layout of the reinforcing in the soil berm, and collateral effects of berm construction on the U-frame lock structure. A non-linear deformation analysis played a central role in addressing all of these questions. Berm construction and four operational load cases were used to understand the performance of the reinforced berm and to discern interactions among the lock, the backfill, the foundation strata of the U-frame lock, the reinforced berm, and the foundation strata of the reinforced berm. Insight gained from the soil–structure–foundation interaction analyses led to an alteration to the proposed reinforcement layout to enhance the performance of the reinforced soil berm.     

Impact of excavation technique on strength of oil shale pillars

Summary The load carrying capacity of oil shale pillars excavated by conventional blasting can be increased significantly by presplit blasting and mechanical mining. Comparisons ofin situ vertical stresses and fractures obtained from overcoring horizontal holes in the Colony Mine, Piceance Creek Basin, Colorado indicate that conventional blasting causes a strength loss in a zone of damage approximately 3 m (10 ft) thick. Presplit blasting reduces damage significantly, and increases the load carrying capacity in the 3 m (10 ft) thick zone by 5.93 MPa (860 psi). Mechanical mining causes little or no rock damage, and an increase of 9.83 MPa (1425 psi) in strength in the same 3 m (10 ft) thick zone. Pillar design using presplit blasting and mechanical mining techniques can increase the extraction ratio by at least 3% and 5%, respectively, as compared to conventional blasting. It is speculated that comparable increases in extraction should also occur due to increases in span dimensions.     

悬挂式防渗墙结合堤后压渗盖重防渗效果的试验研究

在实验室模型槽中进行了有悬挂式防渗墙以及堤后压渗盖重的渗流模型试验,取得了不同贯入度以及不同堤后压渗盖重宽度防止堤基渗透变形的系列试验成果。通过一系列试验结果表明,悬挂式防渗墙和堤后压渗盖重可有效地提高强透水层堤基抵抗渗透变形的能力,且在控制渗透变形向上游发展的作用上功效显著。研究表明,堤后压渗盖重的防渗效益往往低于较大贯入度的防渗墙,但从经济角度来看,不失为一种有效可靠的防渗措施。     

Comparison of Blast-Induced Damage Between Presplit and Smooth Blasting of High Rock Slope

This paper focuses on the comparison of damage induced by smooth blasting and presplit blasting based on the excavation of high rock slope. The whole damage process of the smooth blasting and presplit blasting excavation method is studied by using a cumulative blasting damage numerical simulation technology based on the secondary development of the dynamic finite element code LS-DYNA. The results demonstrate that, in the case of contour blasting with the method of smooth blasting, the total damage of rock slope is a result of cumulated damage induced by the production hole, buffering hole, and smooth hole. Among the total damage, the blasting of the production hole is the main resource, followed by the smooth and buffering holes. For the presplit blasting, the final damage of rock slope is mainly induced by presplit blasting itself. The spatial distribution characteristics of the final damage zone of two methods are compared. Two classes of damage zone could be found in smooth blasting excavation; one of them is the columnar high-degree damage zone around the slope surface and the other is the low-degree damage zone located in the middle of the slope. But in the case of presplit blasting, there is only the columnar high-degree damage zone around the slope surface. Finally, a damage control suggestion for two blasting excavation methods is proposed and verified based on the excavation of the temporary shiplock slopes of the Three Gorges Project in China.     

Model-Based Identification of Mechanical Characteristics of Sinosaurus (Theropoda) Crests

The paired cranial crests of Sinosaurus(Theropoda) have been hypothesized as too weak to resist mechanical loads during combat. Finite element analysis(FEA) is used to test this hypothesis, first with geometry obtained through direct laser scanning of a well-preserved fossil of the crest, and then with two conceptual FE models of both crests analyzing the structure-deformation effects of fenestration. In the original fossil model, under direct loading on the dorsal faces of the crest, we found that the areas surrounding cavities on the crest experience shear stress that implies a high chance of material failure – the fracture of bone. In the conceptual model, a series of computational studies were conducted with varying loading directions. One simulation found that the shear stress and strain in the material around the cavity presented more deformation compared with the conceptual model without the cavities, and under this morphologically realistic scenario the loading conditions would result in local bone fractures. These model-based computational results indicate that the crest could not resist high loads, because it could not effectively decentralize the loading stress. Future investigations need to focus on more comprehensive computational experiments with more conditions, e.g. dynamical loading conditions, and direct palaeontological evidence.     

Role of geology in diamond project development

For a mining operation to be successful, it is important to bring fundamental and applied science together. The mining engineer needs to understand the importance of geology, mineralogy and petrography, and how projects can benefit from the data collected during the exploration and pre-exploration stage. Geological scientists also need to understand the process of project development from the exploration stage through mine design and operation to mine closure. Kimberlite pipe or dyke emplacement, geology and petrology/mineralogy are three areas that illustrate how information obtained from the geological studies could directly influence the mining method selection and the project strategy and design. Kimberlite emplacement is one of the fundamental processes that rely on knowledge of the kimberlite body geology. Although the importance of the emplacement model is commonly recognized in the resource geology, mining engineers do not always appreciate its importance to the mine design. The knowledge of the orebody geometry, character of the contact zones, internal structures and distribution of inclusions could directly influence pit wall stability (thus strip ratio), underground mining method selection, dilution, treatability, and the dewatering strategy. Understanding the internal kimberlite geology mainly includes the geometry and character of individual phases, and the orientation and character of internal structures that transect the rock mass. For any mining method it is important to know “where the less and where the more competent rocks are located” to achieve stability. On the other hand, the detailed facies studies may not be important for the resource and mine design if the rock types have similar physical properties and diamond content. A good understanding of the kimberlite petrology and mineralogy could be crucial not only to the treatability (namely diamond damage and liberation), but also to the pit wall and underground excavation stability, support design, mine safety (mudrush risk assessment) and mine dewatering. There is no doubt that a better understanding of the kimberlite and country rock geology has a direct impact on the safety and economics of the mining operations. The process of mine design can start at the beginning of kimberlite discovery by incorporating the critical geological information without necessarily increasing the exploration budget. It is important to appreciate the usefulness of fundamental geological research and its impact on increased confidence in the mine design. Such studies should be viewed as worthwhile investments, not as cost items.     

Seismic damage of earth structures of road engineering in the 2008 Wenchuan earthquake

To understand the mechanism of the earth structure damage, a wide range of investigations along roads in seismic hazard areas have been carried out after the 2008 Wenchuan earthquake. In this paper, the results from 41 roads investigated are presented, and the 41 roads are located in 7–11 intensity zones and consist of rural/county roads, province roads and state roads in Sichuan province. According to the investigation, the types of damaged slopes and retaining walls are classified and statistical analyses are performed. In the statistical analyses, various impact factors to seismic slope and retaining wall damage were studied, such as slope inclination, height of slope and retaining wall, site conditions, and seismic intensity. In addition, some relationships were developed, including the quantity of damaged slopes with slope inclination and height, the angle between route and fault rupture directions, and site conditions. Finally, some reasonable suggestions are put forward on the designs and constructions of slopes and retaining walls when they are subject to seismic activity.     

Investigation of the integrated retaining system to limit deformations induced by deep excavation

A series of three-dimensional finite element analyses of deep excavations with the integrated system between buttress walls and diaphragm walls was conducted to investigate the effect of the buttress wall intervals, treatments, locations, height, and thickness on limiting deformations induced by deep excavation. The integrated retaining system was formed by maintaining buttress walls when soil was excavated. The wall deflection control mechanism of the integrated retaining system mainly came from the combined stiffness between the buttress wall and the diaphragm wall. In addition, the ground settlement control mechanism came from the combined stiffness between the buttress wall and the diaphragm wall, and the frictional resistance between the buttress wall and the surrounding soil. For achieving 50% reduction in the wall deflection and the ground surface settlement, the length and intervals of buttress walls that were applied to the integrated retaining system were at least 4 and 8 m, respectively. When the deflection at the diaphragm wall head was well restrained, for example, by the floor slab, the position of the buttress wall head could be located at a depth the diaphragm wall starts to bulge out. In such a case, the performance between the full height and limited height of buttress walls was quite close. Furthermore, a new well-documented excavation project was analyzed to verify the performance of the integrated retaining system. Results showed that the integrated retaining system worked excellently if the joints between buttress walls and diaphragm walls were constructed properly.     

地震边坡失稳机理及稳定性分析

通过对汶川地震边坡调研,发现大量边坡破坏形式为坡顶拉裂、下部坡体剪切破坏。本文利用有限差分程序,从边坡土体的应力状态出发,通过监测边坡土体的状态、位移和剪应变增量变化等,分析了岩土体在静力、横向地震和耦合地震作用下的破坏过程,发现坡顶附近发生张破坏,以下部位发生剪切破坏,而非传统的地质工程观点——地震边坡破坏主要是地震惯性力造成的剪切破坏。并提出一种新方法——关键点相对位移法,来判断边坡的动力稳定性,数值模拟结果与已有研究成果及震后灾害调查结果具有良好的一致性。     

Three-dimensional numerical analysis of deep excavations with cross walls

Previous plane strain analysis of a case history has shown that cross walls in an excavation can effectively reduce movements induced by deep excavation. This study performed three-dimensional numerical analyses for 4 deep excavation cases with different installations of cross walls, including different excavation depths, cross wall intervals and cross wall depths. Both the observed and computed wall deflections for the 4 cases were compared with those of the same excavations that were assumed with no cross walls installed to demonstrate the effectiveness of cross walls in reducing lateral wall deflections. The results show that the cross wall also had a corner effect similar to that of the diaphragm wall. The deflection of the diaphragm wall was smallest at the location of the cross wall installed and then increased with the increasing distance from the cross wall, up to the midpoint between two cross walls. Many factors such as in situ soil properties, diaphragm wall properties, construction procedure, cross wall depth and so on may affect the amount of reduction in lateral wall deflections due to the installation of cross walls. Under the same condition, the amount of reduction was highly dependent on the depth of cross walls, distance to the cross walls and the cross wall interval.     

Finite-element 3D modeling of stress patterns around a dipping fault

Stresses in a block around a dipping fracture simulating a damage zone of a fault are reconstructed by finite-element modeling. A fracture corresponding to a fault of different lengths, with its plane dipping at different angles, is assumed to follow a lithological interface and to experience either compression or shear. The stress associated with the destruction shows an asymmetrical pattern with different distances from the highest stress sites to the fault plane in the hanging and foot walls. As the dip angle decreases,the high-stress zone becomes wider in the hanging wall but its width changes negligibly in the foot wall.The length of the simulated fault and the deformation type affect only the magnitude of maximum stress,which remains asymmetrical relative to the fault plane. The Lh/Lfratio, where Lhand Lfare the widths of high-stress zones in the hanging and foot walls of the fault, respectively, is inversely proportional to the fault plane dip. The arithmetic mean of this ratio over different fault lengths in fractures subject to compression changes from 0.29 at a dip of 80°to 1.67 at 30°. In the case of shift displacement, ratios are increasing to 1.2 and 2.94, respectively.Usually they consider vertical fault planes and symmetry in a damage zone of faults. Following that assumption may cause errors in reconstructions of stress and fault patterns in areas of complex structural setting. According geological data, we know the structures are different and asymmetric in hanging and foot walls of fault. Thus, it is important to quantify zones of that asymmetry. The modeling results have to be taken into account in studies of natural faults, especially for practical applications in seismic risk mapping, engineering geology, hydrogeology, and tectonics.     

The problem of revealing the absolute kinematics of the opposite walls of faults

The existing kinematic classification of disjunctive dislocations takes into account only the relative displacements of their walls along the displacement surface in opposite directions. The topic of their absolute displacement has not yet been worked out, either in structural geology or in tectonophysics. As a result of analyzing various structural features, unconventional and often unexpected versions of their absolute displacements were worked out: the displacement of one wall along the displacement surface with an immovable second wall; displacement of both walls along the displacement surface in different (but not opposite) directions; displacement of one or both walls not along the displacement surface. It is imperative to concentrate one’s attention on the geological bodies themselves, and not on the fault boundaries between them, for thorough understanding of the faulting kinematics.     

Simulation analysis of the impacts of underground mining on permafrost in an opencast coal mine in the northern Qinghai–Tibet Plateau

Based on two-dimensional heat-conduction equations with a phase-change component, this study investigates the impact of underground mining on the permafrost environment in an opencast coal mining pit. The dynamics of the maximum thawed and freezing depths at different depths around a borehole wall are determined. The spatial distributions of these dynamics are also determined at different locations of the wall profile. The results show that (1) the maximum freezing depth tends to increase over 100 years; (2) the maximum thawed depth increases along a borehole wall over 100 years. In particular, the maximum thawed depth increases faster near the junctions of permafrost and seasonally frozen soil; (3) due to the small cross section of mining laneways, coal mining does not cause rapid increases in permafrost temperature around borehole walls. Once disturbance to permafrost around a borehole wall decreases, the once-insignificant effect of temperature will become more obvious. Underground mining does have some impacts on permafrost surrounding borehole walls, but it does not cause large areas of deformation due to thermal disturbance.     

采矿巷道围岩变形机制数值模拟研究

研究了大冶铁矿龙洞-62 m、-74 m水平采矿巷道开挖后的二次应力分布及巷道变形机制。首先根据现场工程地质勘查和室内岩石力学试验对巷道围岩进行了工程地质分组和岩石力学参数确定;在此基础上运用FLAC3D数值模拟软件研究了巷道开挖后的应力应变状态,分析了围岩变形机制;并根据-74 m水平采矿巷道的收敛监测数据对比验证了数值模拟结果。研究结果表明,围岩条件不同的采矿巷道其二次应力分布影响范围有所差异,但围岩主应力总体上表现为由巷道边墙中下部位的压应力集中带逐步过渡到拱顶、底板一定范围内的拉应力集中带。     

基于损伤变量的煤层底板采动破坏深度计算

传统采动破坏深度计算中认为底板结构完整,未考虑实际岩体损伤。以淮南潘北矿11113工作面A组煤开采为背景,利用FLAC3D对完整与损伤底板采动应力变化特征进行了分析,推导并计算了底板岩层损伤变量与底板破坏深度。此外,为验证该方法的有效性,对比分析了计算结果与测量结果。结果表明:采动应力的最大值出现在煤壁前后方,底板完整时为14.8 MPa,底板损伤时为17.5 MPa;底板岩层损伤变量D为0.574,基于损伤变量计算得出的底板最大破坏深度为16.15 m,对比并行电法探测结果16.00 m,该方法的计算准确率高。研究结果为快速准确确定底板采动破坏深度提供了一个新思路。      

The Influence of Burden on Blast Vibration

There is a common belief within the blasting community that increasing the burden will increase the blast vibration. In order to test this belief in a direct sense, it would be desirable to fire single blastholes with various burdens and monitor the vibrations at many locations. A review of past literature indicates that such direct tests are rare and only scant data is available. Nevertheless, a detailed analysis of this and associated past work (on small-scale blocks and choke blasts) shows no convincing evidence of an influence of burden on blast vibration. On the other hand, by considering the role of reflected waves in a simple analytical model, reasoning is given to show that the vibration might well be insensitive to burden. In view of the scant data available, it was decided to conduct trials of a direct nature, in which 13 single blastholes were fired to a free face. The burdens chosen were 2.6 m, 5.2 m and 10.4 m, and the vibration was measured at typically 10 locations over the range 5 m to 50 m from each hole. The results clearly show that the vibration is independent of such burdens. Furthermore, a side-by-side comparison of a choke blast with a free-face blast showed that the vibration from the holes in the choke blast was not higher than the vibration from the holes in the free-face blast. The present work also shows that vibration, although insensitive to burden, is not insensitive to the condition (i.e., the degree of damage) of the surrounding rock mass. In this regard, blastholes in undamaged ground produce a significantly higher vibration than blastholes in damaged ground. This might well be the reason why pre splits and drop-cuts are observed to produce relatively high vibrations, i.e., it is not because such blasts typically involve large burdens, but rather that they are usually initiated in relatively undamaged ground.     

Variable Energy Explosives for Soft Ground Blasting

A range of bulk explosives, the NOVALITE range hay been specifically developed for soft ground blasting. These explosives can be used in both wet and dry blasting conditions, range in density from 0.3-1.2 g/cc and range in VoD from 2-4.5 km/s. This range of explosives hay the potential to be tailored to ground type and is predicted to be suitable for a variety of applications which include: blasting in soft to medium overburden, coal blasting, wall control, and low vibration blasting. Trials have been conducted in several applications with encouraging results. Several cast/throw blasts have been conducted with these products partially replacing either ANFO or Heavy ANFO. The results from the blast have been equivalent in cast (per cent) and at reduced cost per unit volume. These products have also been used in presplit blasting and have again achieved equivalent or better results when compared to conventional presplit blasting at a lower cost per unit volume. This product has also been used in a vibration sensitive area replacing traditional explosive products, and generating excellent fragmentation and digging whilst maintaining vibration limits. This new range of products, NOVALITE, has shown great potential in many applications either reducing cost per unit volume, improving wall quality or improving productivity in environmentally sensitive areas.     

江苏省煤炭资源及其找矿潜力分析

江苏省煤炭资源较少，远不能满足经济发展的需要。在分析煤炭地质和资源特征的基础上，对煤炭资源的找矿潜力进行了分析，提出了矿区外围和深部、推覆体下和苏鲁豫皖交界处的空白区找煤的设想。